Complete custom rdoc options example

The example in RDoc::Options was missing an example of adding options to
RDoc::Options by reopening the class.

Pointed out by Michael Granger
Update History for previous commit
Moved doc install complete message from RubyGems

This displays total time taken for RDoc when all documentation is
complete after installing gems.

See rubygems/rubygems#469
Raise an Error on a unterminated heredoc

When processing verbatim blocks RDoc attempts to detect if they are ruby
code.  If the verbatim block contains an unterminated here-document a
NoMethodError would be raised.  This causes RDoc to crash.

Now an RDoc::RubyLex::Error is raised which allows the HTML processor to
create an un-highlighted <pre> element instead.

Reported by darix
Improve checking of markdown extensions

Previously Markdown extensions used symbol to string conversion to check
for markdown extensions.

Now Markdown extensions are checked by using the object from the closure
which is cleaner and creates fewer garbage objects.
Reduce string matching to improve performance

Matching strings in the grammar results in increased method calls which
decreases the speed of the parser.

Expanded use of regular expressions decreased parse time by around 20%
Use regexp to match Markdown NewLine and Spacechar

Like the previous commit, regular expressions speeds up markdown parsing
for ruby 1.8.
Replace kpeg repetition with regular expressions

This slightly improves parsing speed as regexp repetition is faster than
a while loop.
Removed rdoc_tags hoe plugin